and placed between the Flexor carpi ulnaris and Flexor digitorum sublimis. It is accompanied by two venæ comitantes, and is overlapped in its middle third by the Flexor carpi ulnaris; the ulnar nerve lies on the medial side of the lower two-thirds of the artery, and the palmar cutaneous branch of the nerve descends on the lower part of the vessel to the palm of the hand.

(b) At the wrist(Fig. 527) the ulnar artery is covered by the integument and the volar carpal ligament, and lies upon the transverse carpal ligament. On its medial side is the pisiform bone, and, somewhat behind the artery, the ulnar nerve.

Peculiarities.The ulnar artery varies in its origin in the proportion of about one in thirteen cases; it may arise about 5 to 7 cm. below the elbow, but more frequently higher, the brachial being more often the source of origin than the axillary. Variations in the position of this vessel are more common than in the radial. When its origin is normal, the course of the vessel is rarely changed. When it arises high up, it is almost invariably superficial to the Flexor muscles in the forearm, lying commonly beneath the fascia, more rarely between the fascia and integument. In a few cases, its position was subcutaneous in the upper part of the forearm, and subaponeurotic in the lower part.

Branches.The branches of the ulnar artery may be arranged in the following groups:

In the Forearm

Anterior Recurrent.

At the Wrist

Volar Carpal.

Posterior Recurrent.

Dorsal Carpal.

Common Interosseous.

In the Hand

Deep Volar.

Muscular.

Superficial Volar Arch.

The anterior ulnar recurrent artery (a. recurrentes ulnaris anterior) arises immediately below the elbow-joint, runs upward between the Brachialis and Pronator teres, supplies twigs to those muscles, and, in front of the medial epicondyle, anastomoses with the superior and inferior ulnar collateral arteries.

The posterior ulnar recurrent artery (a. recurrentes ulnaris posterior) is much larger, and arises somewhat lower than the preceding. It passes backward and medialward on the Flexor digitorum profundus, behind the Flexor digitorum sublimis, and ascends behind the medial epicondyle of the humerus. In the interval between this process and the olecranon, it lies beneath the Flexor carpi ulnaris, and ascending between the heads of that muscle, in relation with the ulnar nerve, it supplies the neighboring muscles and the elbow-joint, and anastomoses with the superior and inferior ulnar collateral and the interosseous recurrent arteries (Fig. 529).

The common interosseous artery (a. interossea communis) (Fig. 528), about 1 cm. in length, arises immediately below the tuberosity of the radius, and, passing backward to the upper border of the interosseous membrane, divides into two branches, the volar and dorsal interosseous arteries.

The Volar Interosseous Artery (a. interossea volaris; anterior interosseous artery) (Fig. 528), passes down the forearm on the volar surface of the interosseous membrane. It is accompanied by the volar interosseous branch of the median nerve, and overlapped by the contiguous margins of the Flexor digitorum profundus and Flexor pollicis longus, giving off in this situation muscular branches, and the nutrient arteries of the radius and ulna. At the upper border of the Pronator quadratus it pierces the interosseous membrane and reaches the back of the forearm, where it anastomoses with the dorsal interosseous artery (Fig. 529). It then descends, in company with the terminal portion of the dorsal interosseous nerve, to the back of the wrist to join the dorsal carpal net-work. The volar interosseous artery gives off a slender branch, the arteria mediana, which accompanies the median nerve, and gives offsets to its substance; this artery is sometimes much enlarged, and runs with the nerve into the palm of the hand. Before it pierces the interosseous membrane the volar interosseous sends a branch downward behind the Pronator quadratus to join the volar carpal network.

The Dorsal Interosseous Artery (a. interossea dorsalis; posterior interosseous artery) (Fig. 529) passes backward between the oblique cord and the upper border of the interosseous membrane. It appears between the contiguous borders of the Supinator